The present invention relates to a method for determining a reference magnitude, and more particularly, a reference magnitude which indicates the state of a vehicle traveling in reverse and which is determined based on a comparison of at least two measured variable magnitudes.
A method of this type, referred to generally as "situation recognition," is disclosed, for example, in German patent document DE 195 15 051 A1 (U.S. Pat. No. 5,774,821). In accordance with the known method, such situation recognition permits the distinguishing of various travel states, for example, straight forward travel, turning, reverse travel and stopping of a vehicle. Such distinction is required in applications involving a situation-dependent determination of control algorithms for a system which regulates vehicle stability.
The situation recognition method disclosed in the above referred patent document determines the state of reverse travel as a reference magnitude by comparing, for example, the angular yawing speed measured by a sensor with an angular yawing speed calculated from a steering angle measured by another sensor. When the measured angular yawing speed and the calculated angular yawing speed have different signs, and when the derivatives of these magnitudes with respect to time also have different signs, the state of reverse travel is recognized.
In order to convert the magnitudes measured by the sensors in the above example into a usable reference magnitude, several computing steps are necessary. In particular, the known method requires a conversion of the measured steering angle into an angular yawing speed, followed by a differentiation of measured and calculated angular yawing speed with respect to time. In order to ensure reliable recognition of reverse travel and/or good reproducibility of the comparison results, these computing steps, which are normally carried out by a microprocessor, must be carried out with a high degree of computing precision. In addition, a high degree of signal resolution is generally required, i.e., requiring small quantized steps from the sensors and from any downstream analog/digital converters which may be present.
Execution of the computing steps with the required level of computing precision, for example, by implementation of floating-point arithmetic, requires a microprocessor providing high computing capability, or may further require an additional floating-point processor, resulting in increased cost. High-resolution sensors and analog/digital converters are also expensive.
The utilization of simpler calculation methods for implementing the known method, such as integer arithmetic in which the computing steps involve only integer magnitudes, and which would otherwise be desirable because of a lower computing capability requirement, would however lead to computing errors, for example, when the remainder in a division of two magnitudes into each other is simply ignored. Particularly where several computing steps of this kind are used, such computing errors, which would then occur in a cumulative manner, would lead to unsatisfactory results in the determination of a reference magnitude, for example, one indicative of reverse travel.
It is therefore the object of the present invention to provide a method for the determination of a reference magnitude based on a comparison of at least two variable magnitudes, and in which the reference magnitude can be determined with relative reliability using simple computing steps and which may be implemented with inexpensive circuitry.